Chemical Analysis Of Urine: Glucose, Ketone Bodies, Protein
Introduction
The chemical analysis of urine is an essential procedure that can detect various diseases. Urine contains different chemical compositions, and these compositions can change in abnormal or pathological conditions. By examining these changes, diseases can be detected early. The composition of urine depends on the type and quantity of waste material that needs to be excreted from the body. Normal urine composition includes urea, creatinine, uric acid, ammonium salts, chlorides, sulphates, and phosphates of various elements. Abnormal urine constituents, such as glucose, protein, ketone bodies, bilirubin, and bile salts, are not detectable in normal urine, but their presence in urine indicates a pathological condition. For instance, glucose in urine during diabetes mellitus and protein in urine during renal disease are indicative of a pathological condition. Therefore, a chemical examination of urine helps to investigate an individual's health condition.
Objective:
As a student, it is important to have a basic understanding of how to perform chemical tests in order to determine the chemical constituents of various substances. This involves learning the different methods used for analyzing substances and interpreting the results.
1. Glucose in urine ( Glycosuria)
Glucose is the most common sugar found in urine, although other sugars like lactose, fructose, galactose, and pentose can also be found in certain conditions. Normally, there is not enough sugar in urine to react with common enzyme or reducing tests. The presence of sugar in urine indicates an abnormality caused by diabetes mellitus, making urine sugar tests very useful in monitoring the treatment of this disease. To summarize, urine sugar tests are important for managing diabetes as they can detect the presence of glucose in urine, which is an indicator of the disease.
Clinical Significance
Glycosuria refers to the presence of detectable levels of glucose in urine, which is not normal if it exceeds the normal range of 15-20 mg/dl. Typically, the kidneys reabsorb almost all the glucose from the glomerular filtrate into the circulation, but when the blood glucose level becomes too high, excess glucose appears in the urine. This occurs when the renal threshold, the lowest blood glucose level that will result in glycosuria, is exceeded, which is commonly seen in diabetes mellitus. The normal blood glucose level ranges between 65-110 mg/dl, which may increase up to 120-160 mg/dl after a meal.
Causes of Glycosuria
• Physiological
• Pathological
Physiological
Glycosuria can occur in certain physiological situations, which include:
•after consuming a large amount of carbohydrates,
•in response to the stimulation of the sympathetic nervous system (e.g. excitement, stress)
•during pregnancy (in about 15-20% of cases), and
•in cases of renal glycosuria, where the individual experiences glycosuria despite having normal blood glucose levels. Renal glycosuria is typically a harmless condition resulting from a lowered renal threshold.
Pathological
A. Diabetes mellitus
Glycosuria refers to the presence of detectable levels of glucose in urine.
The most frequent cause of glycosuria is diabetes mellitus, which is a metabolic disorder resulting from insulin deficiencies. In diabetes, glucose is not correctly processed, causing an increase in blood glucose levels. When blood glucose levels reach a range of 170 - 180 mg/dL, glucose begins to appear in the urine.
B. Glycosuria due to other endocrine disorders
Endocrine disorders can cause high blood sugar levels known as hyperglycemia. This can lead to the presence of glucose in urine, which is called glycosuria.
Some examples of endocrine disorders that can cause hyperglycemia include: •hyperthyroidism
• hyperadrenalism
• hyperpituitarism
• and certain pancreatic diseases.
2. Determination of Ketone Bodies
Introduction
Ketone bodies, also known as ketones, are three related substances: acetone, acetoacetate, and β-hydroxybutyrate. They are produced during normal fat metabolism in the body. Normally, ketones are not detectable in the blood or urine. When there is a lack of carbohydrates in the diet or an issue with carbohydrate metabolism or absorption, the body metabolizes more fatty acids, which leads to the production of excess acetyl-CoA. This extra acetyl-CoA is then converted into acetoacetic acid, which is mostly reduced to β-hydroxybutyric acid, and some is decarboxylated into acetone. Ketone bodies are transported through the blood to the peripheral tissues to be used as an alternative fuel for cells. In these tissues, they are converted back into acetyl-CoA, and used for energy. Acetone is excreted in the urine.
Clinical Significance
When the production of ketone bodies is higher than their utilization, their levels increase in the bloodstream, known as ketonemia, and eventually in urine, called ketonuria. This condition is commonly observed in individuals with diabetes mellitus and during starvation. Ketonuria may also result from prolonged vomiting, severe diarrhea, high fat intake, low carbohydrate diet, severe liver damage, or anesthesia. Excessive accumulation of ketone bodies can lead to ketosis, which is a serious condition. Acetoacetic acid and β-hydroxybutyric acid contribute to excess hydrogen ions in the blood, leading to acidosis that can decrease the blood pH, and if not treated promptly, can be fatal. Additionally, ketone accumulation can result in brain damage as acetone and acetoacetic acid are toxic to brain tissues. Furthermore, ketones accumulate in the blood and urine at different concentrations.
3. Determination of Urinary Protein
Introduction
Protein is a large molecule made up of one or more chains of amino acids with a specific sequence and weight. It has several crucial functions in biology, including acting as enzymes (e.g., trypsin), transport proteins (e.g., hemoglobin, myoglobin), nutrient and storage proteins (e.g., ovalbumin from eggs, casein from milk), contractile or motile proteins (e.g., actin, myosin), structural proteins (e.g., keratin, fibroin, collagen), defense proteins (e.g., antibodies, fibrinogen), and regulatory proteins (e.g., insulin, growth hormone).
Checking for the presence of protein in urine is an essential and valuable part of routine urine analysis. Albumin is an important protein that appears in urine during pathological conditions, often indicating kidney disease. On the other hand, globulins are excreted less frequently. In multiple myeloma, a specific type of globulin called Bence Jones protein is excreted.
Clinical Significance
Proteinuria refers to the presence of protein in urine and is a significant indicator of kidney disease. The amount of protein in urine can vary depending on the specific clinical and pathological condition and the severity of the disease.
Causes of Proteinuria
1. Increased permeability of the glomerulus
The glomerular membrane is responsible for the initial stage of urine formation and usually does not allow protein molecules to pass through. However, if the glomerular membrane is damaged, these large protein molecules can pass through and enter the urine.
2. A decrease in normal reabsorption in the tubule
Normally, only a small amount of protein with a lower molecular weight passes through the glomerulus and is filtered out. This protein is usually reabsorbed back into the bloodstream, which leads to only a trace amount of protein being present in urine. This small amount is not typically detectable by standard laboratory tests. However, if the body fails to reabsorb the protein from the glomerular filtrate, which makes up 99% of the filtered blood, then large quantities of protein will be present in the urine.
Types of Proteinuria
1.Accidental or false proteinuria: This type of proteinuria occurs when protein mixes with other substances in the urine, such as pus, blood, or vaginal discharge. It is often seen in infections affecting the kidneys, bladder, or vagina.
2. Physiological or functional proteinuria: This type of proteinuria is a normal response to certain physiological conditions such as fever, exposure to extreme temperatures, intense exercise, emotional stress, or late-stage pregnancy. The underlying mechanism that causes proteinuria in these cases is the constriction of blood vessels in the kidneys.
3. Postural (orthostatic) proteinuria: This type of proteinuria occurs when individuals excrete protein while standing or sitting for long periods of time. It is intermittent and usually disappears when the person lies down. It may also be seen in people with abnormal curvature of the spinal cord.
4. Renal or true proteinuria: This type of proteinuria occurs due to a malfunction in the kidney's filtering system, either in the glomeruli or the tubules. As a result, protein from the blood is passed into the urine.
Post a Comment